The present invention relates to a projecting direction control system using an auxiliary detection means such as a seat sensor and a gyro sensor with an art of preventing a blinding glare directed onto oncoming vehicles by an inappropriate correction of an optical axis by a malfunctioning of the auxiliary detection means.
As an instrument for controlling the projecting direction of a vehicle headlamp such that the projecting direction thereof is corrected in response to variation in the vehicle posture, there is a known instrument for automatically adjusting the projecting direction of the headlamp (a so-called auto-leveling instrument) so that the projecting direction of the headlamp is held in a predetermined state even when the inclination of the vehicle changes. When applied to a headlamp system affording a large quantity of light with a discharge lamp as a light source, such an instrument is effective in improving safety as glare is prevented from being directed onto oncoming vehicles.
In an instrument of the sort mentioned above, as disclosed in JP-A-10-226271 (Japanese Application Publication Number: Hei10-226271), JP-A-10-230777 (Japanese Application Publication Number: Hei10-230777) and JP-A-2001-080409 (Japanese Application Publication Number: 2001-080409), for example, the height value of a front-wheel axle portion is presumed or estimated from the information obtained by one height-detecting means (height sensor) provided in the rear-wheel axle portion of a vehicle, and the pitch angle of the vehicle is then obtained so as to drive the reflecting mirror of a lighting device to negate the variation of the pitch angle whereby to perform correction control in order that the angle-to-ground of an optical axis of projection light is kept at a regular angle.
In a system of estimating the vehicle posture using the information obtained by one height-detecting means, as it is needed to suppress dazzling light causing glare on taking into consideration an entire load condition (e.g., a passenger loadfactor, a carrying condition, etc.). Therefore, an optical axis of light projected from a headlamp is often controlled so that the optical axis thereof is tilted slightly downward with respect to the horizontal plane in view of not bringing about glare even in a normal load condition (e.g., only a driver is on board), and this is unsatisfactory as viewed from the forward visibility of the driver.
In order to the solve the problem above, an arrangement using an auxiliary detection means for detecting the load condition as described below, for example, is conceivable.                A system utilizing auxiliary signals detected by a seat sensor, a seat-belt sensor and the like for detecting the presence or absence of a person seated in the passenger seat.        A system utilizing auxiliary signals detected by a gyro sensor, a G sensor and the like.        
In any one type of system above, variations in the load condition and in the inclination of the vehicle are detected by the auxiliary detection means and control of the optical axis of projection light is performed in response to the variations.
In the conventional projecting direction control systems, however, control of the optical axis of light projected from the headlamp may not properly be performed in case that the auxiliary detection means is troubled from reasons such as a breaking down of a wire or an electrically non-connected condition by a dislocated connector. Consequently, it is feared that dazzling light toward oncoming vehicle drivers and road users becomes conspicuous.
While the seat sensor is functioning properly with a person seated in the passenger seat, for example, an additional load is applied to the front-wheel axle portion as compared with a case where only a driver is on board. Therefore, the projecting direction control system makes correcting calculation by detecting the sinking of the forepart of the vehicle from the height information obtained and controls the direction of the optical axis of projection light on the basis of the calculated result. However, in case the seat sensor is in an abnormal state or in a malfunctional state, the correction of the optical axis of projection light without matching the actual load condition is made in that a person is detected as seated in the passenger seat though no one is actually seated in the passenger seat. On the other hand, no one is conversely detected as seated in the passenger seat though a person is actually seated in the passenger seat, whereby there is the possibility that an unexpected control condition occurs and consequently brings about glare.